Inflammation occurs as a result of tissue damage. This tissue damage can be from microbial invasion, autoimmune processes, tissue infection, allograft rejection, or such hurtful or destructive external influences as heat, cold, radiant energy, electrical or chemical stimuli, or mechanical trauma. Whatever the cause or bodily site, the inflammatory response is quite similar, consisting of a complicated set of functional and cellular adjustments, involving the microcirculation, fluid shifts, and inflammatory cells (leukocytes). When tissue damage occurs, soluble chemical substances are elaborated which initiate the inflammatory response.
The inflammatory response consists of a complex series of events that may be summarized as follows. (1) A local increase in blood flow, with capillary dilatation and increased permeability to the fluid components of the blood. (2) A localized exudation of fluid at the site of injury, including the proteins of the plasma that normally leave the capillaries at a relatively low rate. (3) The exudation of leukocytes from the capillaries into the inflammation site. This exudate initially consists primarily of polymorphonuclear leukocytes, followed by monocytes, lymphocytes, and plasma cells. These leukocytes produce a variety of mediators that control the extent and duration of the inflammatory response, and have a series of receptors on their surfaces available to react to the host of chemical mediators and proteins that are part of the inflammatory fluid. Such leukocyte receptor-mediator or protein interactions are important in controlling leukocyte function within the inflammatory site.
The identification and characterization inflammation is an important part of medical and veterinary practice. In the case of infectious causes of inflammation, it is frequently necessary to search for “hidden sites of inflammation” in individuals who present with clinical syndromes no more specific than fever and weight loss. Similarly, in patients with autoimmune disease such as rheumatoid arthritis or allograft rejection as causes of inflammation, identification of the site(s) and extent of inflammation and its changes with therapy are an important part of medical and veterinary practice. Not surprisingly, then, much effort has been expended and many techniques developed in an attempt to assess the site(s) and extent of the inflammatory process. These techniques include conventional x-ray techniques, computerized axial tomographic scanning (CAT scanning), and a variety of radionuclide scans. See Sutton, A Textbook of Radiology and Imaging, 3rd Ed., Churchill Livingston, 1980: Clinical Nuclear Medicine, Maysey et al., ed., W. B. Sanders, 1983.
One area of difficulty for medical practitioners involves distinguishing between bacterial and viral infections in patients that exhibit many symptoms of either type of infection (e.g. fever, flu-like symptoms, etc.). However, quick, reliable means for assessing whether anti-bacterial drug or an anti-viral drug should be administered are not available. Hence, new methods for distinguishing bacterial infections from viral infections are needed.